Regioselective hydroformylation of vinyl acetate catalyzed by rhodium complex of naphthyl-based monodentate bulky phosphine and phosphite ligands

Article abstract of DOI:10.1016/j.apcata.2012.01.027

The hydroformylation of vinyl acetate was carried out using rhodium complex of naphthyl-based monodentate bulky phosphine and phosphite ligands. All the naphthyl-based ligands favored the formation of desire branched aldehyde. High turnover frequency with excellent regioselectivity to branched aldehyde and high selectivity to aldehyde were observed with bulky phosphite ligands. The effect of partial pressure of CO and H₂, concentration of vinyl acetate, stirring rate and solvents on the hydroformylation of vinyl acetate catalyzed by Rh/bulky phosphite were examined precisely in order to improve the catalytic activity and selectivity. In contrast to conventional organic solvents, the significant influence on the activity and selectivity was observed in organic carbonates ('green' solvent) particularly in propylene carbonate (PC). The PC/catalyst system could be recycled without significant loss of activity and selectivity.

Full text of DOI:10.1016/j.apcata.2012.01.027

Applied Catalysis A: General 419–420 (2012) 185–193
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Regioselective hydroformylation of vinyl acetate catalyzed by rhodium complex
of naphthyl-based monodentate bulky phosphine and phosphite ligands
Aasif A. Dabbawala, Hari C. Bajaj∗, Ganga V.S. Rao, Sayed H.R. Abdi
Discipline of Inorganic Materials and Catalysis, Central Salt and Marine Chemicals Research Institute (CSIR-CSMCRI), Council of Scientific and Industrial Research, G. B. Marg, Bhavnagar
364002, Gujarat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 June 2011
Received in revised form 19 January 2012
Accepted 21 January 2012
Available online 30 January 2012
The hydroformylation of vinyl acetate was carried out using rhodium complex of naphthyl-based mon-
odentate bulky phosphine and phosphite ligands. All the naphthyl-based ligands favored the formation
of desire branched aldehyde. High turnover frequency with excellent regioselectivity to branched alde-
hyde and high selectivity to aldehyde were observed with bulky phosphite ligands. The effect of partial
pressure of CO and H2, concentration of vinyl acetate, stirring rate and solvents on the hydroformylation
of vinyl acetate catalyzed by Rh/bulky phosphite were examined precisely in order to improve the cat-
alytic activity and selectivity. In contrast to conventional organic solvents, the significant influence on
the activity and selectivity was observed in organic carbonates (‘green’ solvent) particularly in propy-
lene carbonate (PC). The PC/catalyst system could be recycled without significant loss of activity and
selectivity.
Keywords:
Hydroformylation
Vinyl acetate
Monodentate bulky phosphite
High rate
© 2012 Elsevier B.V. All rights reserved.
Regioselective
1. Introduction
[12–14]. Recently, regioselective hydroformylation of functional-
ized alkenes such as alkyl acrylate, allyl cyanide, allyl alcohol,
Catalytic hydroformylation is an elegant method to prepare
wide range of aldehydes in a single step by the reaction of olefins,
CO and H2 with high selectivity [1,2]. It is mainly used for the
preparation of bulk and specialties chemicals. The application of
this process has also been extensively explored in pharmaceutical
and fine chemical synthesis [1–6]. This powerful atom efficient pro-
cess is very attractive however; simultaneous control of activity and
selectivity (chemo- as well as regioselectivity) is one of the impor-
tant issue and concern of hydroformylation. Rhodium complexes of
modified phosphorous containing ligands display high activity and
selectivity for the hydroformylation of olefins under mild reaction
conditions. The steric and electronic properties of ligands play an
imperative role in concern to activity and selectivity of hydroformy-
lation catalysts. As a result, varieties of modified monodentate and
bidentate phosphine/phosphite ligands have been synthesized by
fine tuning their electronic and steric properties to address the
issues of activity and selectivity [7–11].
enamide and vinyl acetate [19] have also received attention.
Hydroformylation of such substrates offers products having two
functional groups widely used in organic syntheses [15–19]. Par-
ticularly, the hydroformylation of vinyl acetate provides gate way
to valuable building blocks for the preparation of bifunctional inter-
mediate which can be further converted into synthetically useful
compounds such as 1,2- and 1,3-propanediol, lactic acid and ethyl
lactate (Scheme 1).
Indeed, vinyl acetate, less reactive to syngas in comparison to
terminal alkenes requires high pressure to achieve high turnover
frequency [20], also suffers from a low selectivity and forma-
tion of by-products [21]. However, there are few reports wherein
hydroformylation of vinyl acetate is carried out under mild con-
ditions with good regioselectivity [22–24]. The hydroformylation
reaction proceeds even at 2 atm pressure and 80 ◦C in the pres-
ence of diphosphines in the rhodium complex with large excess of
triphenyl phosphine (PPh3) and resulted in the vinyl acetate con-
version from 38 to 60% with branched aldehyde regioselectivity
from 53 to 82% [22]. Abatjoglou et al. reported vinyl acetate hydro-
formylation at low pressure and temperature (8.4 atm, 60 ◦C) with
branched aldehyde regioselectivity from 77 to 86% depending on
the phosphine and solvent used [23]. Trzeciak and Ziółkowski also
demonstrated vinyl acetate hydroformylation at 1 atm and 40 ◦C by
rhodium/triphenyl phosphite catalyst system [24]. In above cases,
the regioselectivity was achieved but at the expense of the reac-
tion rate. In consequent, over past decades, a great deal of efforts
Hydroformylation reaction has been mainly studied for ter-
minal and internal olefins. The selective preparation of the
linear aldehyde, the starting material for a variety of polymers,
detergents, cosmetics and other widespread products by hydro-
formylation of terminal and internal alkenes have been reported
∗
Corresponding author. Tel.: +91 278 2471793; fax: +91 278 2566970.
E-mail address: hcbajaj@csmcri.org (H.C. Bajaj).
0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2012.01.027

186
A.A. Dabbawala et al. / Applied Catalysis A: General 419–420 (2012) 185–193
Aldehydes
O
O
O
CHO
CHO
Catalyst
+
+
CO + H2
O
O
O
Temp.
Pressure
3-acetoxypropanal
2-acetoxypropanal
Vinylacetate
(b)
(l)
CH2OH
CH2OH
HO
O
HO
1,2 PDO
1,3 PDO
(i) H2
(ii)Hydrolysis
(i) H2
(ii) Hydrolysis
COOH
CHO
O
i)Oxi.
ii) Hydrolysis
CHO
HO
Lactic acid
O
+
O
2-acetoxy propanal
3-acetoxypropanal
i)Oxi.
ii) trans-esterification
COOEt
HO
Ethyl lactate
Scheme 1. Hydroformylation of vinyl acetate with its application.
has been put to increase the regioselectivity as well as reaction rate;
and to decrease the undesired side products [25–27]. Thus far, there
are a few examples of successful catalytic system which exhibited
high regioselectivity together with rate enhancement. High reac-
tion rate were obtained when the hydroformylation was carried
out with bidentate ligands or with electron-deficient ligands such
as bulky phosphite ligand [26,27].
We have recently reported the synthesis and use of the
monodentate bulky phosphite ligand, tri-1-naphthylphosphite,
P(ONp)3 [28]. Rhodium complex of P(ONp)3 showed high activity
with high selectivity to aldehyde for the hydroformylation of vinyl
acetate [29]. In the present paper, we have synthesized a series of
naphthyl-based monodentate bulky phosphine and phosphite lig-
ands and discussed the steric and electronic effect of ligands on the
reaction rates and selectivity during hydroformylation reaction. In
order to improve activity and selectivity, the effect of partial pres-
sure of CO and H2, concentration of vinyl acetate, stirring rate and
solvents on the hydroformylation of vinyl acetate were examined
in detail. Moreover, the hydroformylation of vinyl acetate using
Rh/bulky phosphite system was also carried out in the organic
carbonates ‘green solvent’. The significant advantages of organic
carbonate are emphasized compared to the conventional organic
solvents along with recycling of the catalyst.
2. Experimental
2.1. Materials
The ligand synthesis was performed using standard Schlenk
technique under nitrogen atmosphere. Tetrahydofuran (THF) was
distilled from sodium/benzophenone prior to use. Toluene,
dichloromethane, and cyclohexane were purchased from
Sigma–Aldrich as anhydrous grade material and used as received.
Et3N was distilled from sodium and stored under N2. PCl3 and
1-bromo naphthalene were obtained from s. d. fine chemi-
cals, India, and used as received. Rh(acac)(CO)2, PPh3, P(OPh)3,
tricyclohexylphosphine PCy3, (p-CF3-C6H4)3P, 1-naphthol, 5,6,7,8-
tetrahydro-1-naphthol, p-chloro-1-naphthol, n-BuLi (1.6 M
solution in hexane), vinyl acetate, PC and dimethyl carbonate
(DMC) were purchased from M/s Sigma–Aldrich Chemicals, USA
and used as received. The syngas (99.9%) used was from Hydro Gas
India Pvt Ltd., India.
2.2. Instrumentation
All the hydroformylation reactions were performed in 100 mL
stainless steel autoclave reactor (Autoclave Engineers, EZE–Seal

A.A. Dabbawala et al. / Applied Catalysis A: General 419–420 (2012) 185–193
187
Cl
O
O
O
O
O
O
O
P
O
O
P
P
P
Cl
Cl
P(ONp)
PNp3 (L1)
3 (L2)
(L3)
(L4)
Scheme 2. The naphthyl-based monodentate bulky phosphine and phosphite ligands.
Reactor, USA). 31P NMR spectra of ligand and complex were mea-
sured in CDCl3 solvent and 85% H3PO4 as an internal reference, on
Bruker Avance 500 MHz FT-NMR. IR spectra were recorded using
nujol mull and KBr pellet on Perkin-Elmer spectrum GX FT-IR sys-
tem in the range 400–4000 cm−1 with a resolution of 4 cm−1. CHN
analysis has been done on Perkin-Elmer, 2400 C, H, N, S/O analyzer.
Products were analyzed with Shimadzu GC-17A gas chromatograph
(GC) using flame ionization detector (FID) having 5% diphenyl- and
95% dimethyl siloxane capillary column (60 m length, 0.25 mm
diameter). Column temperature was initially kept at 50 ◦C for 5 min
and then raised to 200 ◦C at 10 ◦C/min. Nitrogen was used as a car-
rier gas (1.2 mL/min). n-decane was used as internal standard and
the GC was also calibrated using known amount of corresponding
aldehydes.
130.96 ppm, 1H NMR (CDCl3): ı 6.5–6.9 ppm (m, 3H), 2.78 (dt, 4H),
1.69 (m, 4H) and for L4, 31P NMR (CDCl3): ı 129.28 ppm, 1H NMR
(CDCl3): ı 6.8–8.4 ppm (m, 6H, aromatic).
2.4. Synthesis of Rh–P(ONp)3 complexes
Rhodium complexes of type Rh(acac)(CO)L and Rh(acac)L2 were
obtained according to literature procedure [10]. The rhodium
complexes of P(ONp)3 were synthesized from Rh(acac)(CO)2
by varying ligand to Rh mmol ratio. For the synthesis of
rhodium complex of type Rh(acac)(CO)L, an equimolar amounts of
P(ONp)3 (0.019 mmol) was added to the solution of Rh(acac)(CO)2
(0.019 mmol) in toluene (prepared under inert atmosphere). Evo-
lution of CO was observed immediately and the mixture stirred
for 5 min afforded rhodium complex Rh(acac)(CO)L. While addition
of (0.042 mmol) of P(ONp)3 yielded rhodium complex, Rh(acac)L2.
The in situ prepared rhodium complexes using different concentra-
tion of P(ONp)3 were characterized by FT-IR and 31P NMR without
isolation. Spectroscopic characterizations of the rhodium com-
plexes are summarized in Table 1.
2.3. Synthesis of ligands and characterization
The bulky phosphine, tri-1-naphthylphosphine PNp3 (L1) has
been synthesized from 1-bromonaphthalene according to reported
procedure [30,31]. In typical synthesis of PNp3, a dried Schlenk flask
was charged with 7.09 g (34.25 mmol) of 1-bromonaphthalene in
THF (30 mL) under inert atmosphere. A solution of n-BuLi (22.5 mL
of a 1.6 M solution in hexane, 35.97 mmol) was added drop wise
under stirring at −78 ◦C. The reaction mixture was stirred for
1 h, during this period the temperature of the reaction mixture
increased from −78 ◦C to 0 ◦C; and the color of the reaction mixture
changed to orange. To this the solution of PCl3 (1 mL, 11.42 mmol) in
10 mL of THF was added slowly at 0 ◦C over 10 min and stirred addi-
tionally for 5 h at 0 ◦C. After 5 h, the mixture was allowed to warm to
room temperature; precipitated out inorganic salt was filtered off
and washed with dry THF (2 × 10 mL). The combine filtrates were
evaporated in vacuo yielding crude ligand as yellow solid and puri-
fied by recrystallization (from ethanol/hexane). Yield: 1.5 g, 32%.
31P NMR (CDCl3): ı – 31.2 ppm, 1H NMR (CDCl3): ı 7.0–8.2 ppm (m,
7H, aromatic).
2.5. Catalytic reaction
In a typical hydroformylation experiment, required amount of
catalyst, ligand, substrate, solvent were charged into 100 mL auto-
clave. The reactor was flushed with nitrogen three times followed
by flushing syngas twice at room temperature after which reactor
was brought to reaction temperature and pressurized with syngas
at desired pressure. The reaction was initiated by stirring; reaction
started immediately as evidenced by a pressure drop and accompa-
nied increase of the temperature. After desired reaction time, the
stirring was stopped, reactor was cooled down to room temper-
ature, depressurized, flushed with N2 and opened to collect final
sample for GC analysis.
The initial turnover frequency (TOFi) was calculated within
30–40% conversion of vinyl acetate, to avoid inference from the
products. The TOF is defined as:
The bulky phosphite ligand, P(ONp)3 (L2) was synthesized as
per reported procedure [28]. The other bulky phosphites, tris
(5,6,7,8-tetrahydro-1-naphthyl) phosphite (L3) and tris (p-chloro-
1-naphthyl) phosphite (L4) (Scheme 2) were synthesized following
the similar procedure as for P(ONp)3 using 5,6,7,8-tetrahydro-1-
naphthol and p-chloro-1-naphthol. For L3, 31P NMR (CDCl3): ı
number of moles of product form
TOF =
number of moles of rhodium × h
Table 1
Spectroscopic data for rhodium complexes at different P(ONp)3 molar ratios.
1
Entry
L:Rh
Rh-complex
31P{ H} NMR
FT-IR ꢀCO (cm−1
)
ı (ppm)
JP-Rh (Hz)
1
2
3
4
Free ligand
(1:1)
(2.2:1)
(3:1)
–
130.8
–
291
301
301
–
2009
–
Rh(acac)(CO)L
Rh(acac)L2
Rh(acac)L2
120.86
124.37
124.69
–
L: P(ONp)3.

188
A.A. Dabbawala et al. / Applied Catalysis A: General 419–420 (2012) 185–193
Fig. 1. 31P NMR of P(ONp)3 ligand (a) and Rh–P(ONp)3 complexes at different concentration of P(ONp)3; (b) Rh:P(ONp)3 (1:1); (c) Rh:P(ONp)3 (1:2.2) and (d) Rh:P(ONp)3
(1:3).
3. Results and discussion
resulting solution displayed only one vibration band in carbonyl
region at 2009 cm−1 whereas a doublet appeared at ı 120.86 ppm
in 31P NMR while signal at ı 130.8 ppm due to free ligand disap-
pear (Fig. 1). These spectroscopic data corroborate the coordination
of P(ONp)3 to rhodium; and the formation of Rh(acac)(CO)L com-
plex (L = P(ONp)3). The reaction of Rh(acac)(CO)2 with different
phosphorous containing ligands has been studied well as rhodium
complex of type Rh(acac)(CO)P plays an important role to under-
stand the ␴-donor and ␲-acceptor behavior of P ligands [10].
The observed CO stretching frequency at high wave number
(ꢀCO, 2009 cm−1) in the case of Rh(acac)(CO)(P(ONp)3) compare
to the Rh(acac)(CO)PPh3 (ꢀCO, 1975 cm−1) indicates weak ␴- and
strong ␲-acceptor behavior of P(ONp)3. With higher excess of
P(ONp)3 (ligand/Rh > 2), the further CO substitution occurred and
the resulting reaction solution gave no band in CO region and
signal at ı 120.86 ppm was shifted to ı 124.37 ppm in 31P NMR
(Fig. 1) confirming the formation of complex of type Rh(acac)
(CO)L2.
3.1. Characterizations
Invariably the active rhodium catalyst for hydroformylation
reaction is generated in situ using Rh(acac)(CO)2 as rhodium source.
In present study, the rhodium catalysts used for hydroformylation
of vinyl acetate were also generated in situ from Rh(acac)(CO)2
and ligands. However, to confirm the coordination of P(ONp)3
to rhodium and to understand the ligand exchange process, the
P(ONp)3 was added to a solution of Rh(acac)(CO)2 with different
ligand to rhodium molar ratio and the formation of rhodium com-
plexes with P(ONp)3 were probed by FT-IR and 31P NMR (Table 1).
The 31P NMR of free P(ONp)3 gave signal at ı 130.8 ppm while
infrared spectra of Rh(acac)(CO)2 displayed two band in carbonyl
region, one at 2007 cm−1 and another at 2089 cm−1. The addition
of equimolar amounts of P(ONp)3 to Rh(acac)(CO)2, the substi-
tution of the CO occurred immediately. The infrared spectra of

A.A. Dabbawala et al. / Applied Catalysis A: General 419–420 (2012) 185–193
189
O
O
Hydrolysis
O
+
OH
OH
Ethanol
Ethyl acetate
Acetic acid
H2
Aldehydes
CHO
O
O
O
Rh(CO)2acac/L
CHO
+
CO + H2
+
O
O
O
Vinyl acetate
2-acetoxy propanal
3-acetoxy propanal
hydrogenolysis
Decomposition
O
O
Hydorformylation
H2
CHO
+
CHO
Propanal
Scheme 3. Decomposition pathway of vinyl acetate hydroformylation.
OH
+
OH
Acetic acid
Acetic acid
Acrolein
Ethylene
3.2. Influence of steric and electronic nature of ligands on
hydroformylation of vinyl acetate
high regioselectivity but low activity as compare to PPh3 (Table 2,
entries 2 and 3). However the initial rate of vinyl acetate hydro-
formylation was better compared to unmodified Rh(acac)(CO)2
catalyst. This result clearly indicates that the steric nature of ligands
remarkably influences the regioselectivity to branched aldehyde.
The rhodium complex modified with phosphite ligands displayed
high TOF as well as high selectivity. In fact, an excellent regiose-
lectivity (99%) for the preferred branched aldehyde and selectivity
to aldehyde (93%) with high TOF were attained with monodentate
bulky phosphite ligands (Table 2). The P(OPh)3 gave high TOF than
phosphines but lower than bulky phosphites ligands. Among the
naphthyl-based bulky phosphite ligands, P(ONp)3 afforded notable
catalytic activity (Table 2, entry 5). The observed TOF is ∼1.7 times
higher compared to the Rh/P(OPh)3 catalytic system. These results
clearly demonstrate that the ligands having ␲-acceptor ability
along with high steric nature enhance reaction rate and selectivity
considerably.
The selection of an appropriate ligand is one of the critical
issues in the transition metal catalyzed hydroformylation reac-
tions as ligands play significant role in the activity and selectivity.
Earlier we screened variety of P ligands for rhodium catalyzed
hydroformylation of vinyl acetate [29]. It was found that at opti-
mum conditions (temperature 90 ◦C, syngas pressure 4.0 MPa),
the steric and electronic nature of ligands remarkably influences
the regioselectivity to branched aldehyde and catalytic activity.
Rhodium complex modified with P(ONp)3 ligand having high steric
nature and strong ␲-acceptor ability effectively catalyzed hydro-
formylation of vinyl acetate with high regioselectivity (99%) to the
preferred branched aldehyde with notable high turnover frequency
[29]. Thus, to study the influence of naphthyl-based P ligands on
the hydroformylation of vinyl acetate, the various naphthyl-based
monodentate bulky phosphine and phosphite ligands were syn-
thesized (Scheme 2). The rhodium catalyst was prepared in situ
by mixing the appropriate amounts of ligand with Rh(acac)(CO)2.
The hydroformylation was carried out with ligand/Rh ratio of 6
using 0.23 mmol/L Rh(acac)(CO)2. The reaction products were 2-
acetoxypropanal and 3-acetoxypropanal along with acetic acid and
ethyl acetate as side products (Scheme 3).
In order to perceive whether further improvements are possi-
ble in activity and selectivity using Rh/P(ONp)3, the effect of partial
pressure of CO and H2, concentration of vinyl acetate, stirring rate
and solvents on the hydroformylation of vinyl acetate were exam-
ined.
3.3. Effect of partial pressure of pCO and pH2
The naphthyl-based P ligands were then evaluated for the
rhodium catalyzed hydroformylation of vinyl acetate (temperature
90 ◦C, syngas pressure 4.0 MPa). The PPh3 and P(OPh)3 were taken
as reference ligands in this study. The rhodium complex modified
with monodentate bulky phosphine ligand PNp3 (L1) resulted in the
It is established that the hydroformylation of vinyl acetate pro-
ceeds slowly at low syngas pressure and minimum 4.0 MPa syngas
pressure is require to achieve reasonable TOF [29]. As a conse-
quence, the effect of CO partial pressure on the vinyl acetate
Table 2
Influence of various ligands on the hydroformylation of vinyl acetate.a
Entry
Ligand
Conv. (%)
Time (min)
TOFib (h−1
)
Saldehyde (%)
b/l
1
–
12
28
15
30
34.5
34
32
60
30
60
15
10
10
10
480
2240
600
4800
8280
8160
7680
89
92
82
93
93
94
93
95/5
93/7
99/1
92/8
99/1
99/1
99/1
2c
3
PPh3
PNp3
P(OPh)3
P(ONp)3
L3
4c
5c
6
7
L4
a
Reaction conditions: Sub/cat., 4000; [Rh(CO)2acac], 0.23 mmol/L; P/Rh, 6.0; temperature, 90 ◦C; syngas pressure (1:1), 4.0 MPa; solvent (toluene), 50 mL.
Turnover frequency, determined based on 30–35% GC conversion.
Reported earlier, Ref. [29].
b
c

190
A.A. Dabbawala et al. / Applied Catalysis A: General 419–420 (2012) 185–193
Table 3
Effect of partial pressure of pCO and pH2 on Rh/P(ONp)3 catalyzed hydroformylation of vinyl acetate.a
Entry
pCO (bar)
pH2 (bar)
Conv. (%)
TOF (h−1
)
Saldehyde (%)
b/l
1
2
3
4
5
6
7
15
25
35
45
15
15
15
15
15
15
15
25
35
45
23.5
21.5
19.0
15.0
40.0
54.0
67.5
5640
5160
4560
3600
9600
92.0
93.0
92.0
93.0
93.0
93.0
92.0
98/2
99/1
99/1
99/1
99/1
99/1
99/1
12960
16200
a
Reaction conditions: [vinyl acetate], 0.93 mol/L; [Rh(CO)2acac], 0.23 mmol/L; P/Rh, 6.0; temperature, 90 ◦C; solvent (toluene), 50 mL; reaction time, 10 min.
hydroformylation was studied at 90 ◦C and constant H2 partial pres-
sure (1.5 MPa) by varying the CO partial pressure (2.5–4.5 MPa). The
TOF of vinyl acetate hydroformylation decreased with an increase
of CO partial pressure (Table 3, entries 2–4) exhibiting an inverse
dependency on CO partial pressure. The rate inhibition trend at
higher CO partial pressure, common characteristic of hydroformy-
lation catalyzed by rhodium complexes modified with P ligands
[32] is mainly due to the formation of inactive acyl species (H)
(Fig. 5) at higher CO partial pressure. The species (H) is in equi-
librium with the catalytic species (F) and is affected by CO partial
pressure. The equilibrium can shift from (F) to (H) significantly at
higher CO partial pressure resulted in the lower TOF.
The effect of H2 partial pressure on the vinyl acetate hydro-
formylation was studied at 90 ◦C, at constant CO pressure (1.5 MPa)
by varying the H2 partial pressure (2.5–4.5 MPa). The TOF of vinyl
acetate hydroformylation increased linearly on increasing the par-
tial pressure of hydrogen indicating first order dependency on H2
partial pressure (Table 3). This trend indicates that the oxidative
addition of hydrogen to the acylrhodium intermediate (F) would
be a rate determining step (Fig. 5). In all conditions, the chemo
selectivity to aldehyde and regioselectivity to branch aldehyde (2-
acetoxypropanal) were unaffected.
(from 0.93 to 1.63 mol/L) indicating substrate inhibition trend. The
similar substrate inhibition has been reported in the hydroformyla-
tion of vinyl acetate using HRh(CO)(PPh3)3 as catalyst [32]. Gener-
ally, a positive order dependency with respect to olefin concentra-
tion has been observed up to a critical substrate/catalyst ratio, after
that a negative or zero dependence was observed. The similar trend
observed in a present system is mainly due to the coordination of
the substrate to the rhodium catalyst (Fig. 5, species E and E2) in
which carbonyl group of vinyl acetate coordinates with rhodium to
form chelates. At higher vinyl acetate concentration, the rhodium
catalyst present in the chelates form which resulted in the decrease
in TOF. The variation of the initial vinyl acetate concentration
scarcely influenced the selectivity to branched aldehyde and selec-
tivity to aldehyde. Moreover, in order to ascertain that high selectiv-
ity is maintained throughout the course of the reaction, the hydro-
formylation reaction was studied till the complete consumption of
vinyl acetate. At regular intervals, the samples were collected and
analyzed by GC. The kinetic profile for the Rh/P(ONp)3 catalyzed
hydroformylation of vinyl acetate showed the gradually increase
of conversion with time (Fig. 3). The complete conversion of vinyl
acetate was at 50 min while selectivity (chemo- as well as regio)
was high from the beginning and remained almost unaffected
throughout the course of the reaction (Fig. 3). Also, the acrolein
(form due to the decomposition of 3-acetoxypropanal, Scheme 3)
was not detected in GC analysis. This signifies that no decomposi-
tion of 3-acetoxypropanal occurred confirming high regioselectiv-
ity observed in present study was mainly due to the nature of ligand.
3.4. Effect of initial vinyl acetate concentration
The effect of vinyl acetate concentration on the rate of hydro-
formylation was studied at 90 ◦C, 4.0 MPa syngas pressure and
ligand/Rh of 6.0 by varying the vinyl acetate initial concentra-
tion (0.7–1.63 mol/L). The TOF of vinyl acetate hydroformylation
increased at lower vinyl acetate concentration, particularly from 0.7
to 0.93 mol/L (Fig. 2) whereas it decreased at higher concentration
3.5. Effect of stirring rate
In order to see the impact of gas liquid mass transfer resis-
tance, the effect of agitation speed on the TOF and selectivity of
8500
8400
8300
8200
8100
8000
7900
7800
100
80
Conversion
Selec.ald.
60
Selec.branched ald.
40
20
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0
10
20
30
40
50
Conc. of vinyl acetate
(mol/L)
Time (min)
Fig. 2. Effect of initial vinyl acetate concentration on Rh/P(ONp)3 catalyzed hydro-
Fig. 3. The kinetic profile of the rhodium catalyzed vinyl acetate hydroformylation
formylation of vinyl acetate.
using ligand P(ONp)3.

A.A. Dabbawala et al. / Applied Catalysis A: General 419–420 (2012) 185–193
191
proceeds well with high activity and selectivity (Table 4, entries
1 and 2). While catalytic activity was low in tetrahydrofuran and
dichloromethane (DCM) (Table 4, entries 3 and 4) with comparable
aldehyde selectivity and regioselectivity. The reaction performed
in these commonly used solvents present several drawbacks like
toxicity, volatility and high flammability. Subsequently, ionic liq-
uids have been used widely as alternative solvents [33–35]. The
recent research focused is on the use of organic carbonates (as
green solvent) for catalysis [36–39] particularly cyclic carbonates
(propylene carbonate, PC) which display some remarkable prop-
erties like high boiling point, odorless, low toxicity, low viscosity,
noncorrosive, inflammable and biodegradable [36–39]. The PC has
been used as solvent for the asymmetric hydrogenation [36,38],
asymmetric allylic alkylation, amination [37], and in sonogashira
reaction [40]. Thus, we have investigated the viability and ben-
eficial effect of organic carbonate as solvent in hydroformylation
of vinyl acetate catalyzed by Rh/bulky phosphites. The significant
influence of organic carbonates as solvent on the catalytic activity
and selectivity can be seen by comparing results summarized in
Table 4. In particular, the high TOF with high selectivity for alde-
hyde and comparable regioselectivity to branched aldehyde was
achieved when the reactions were performed in PC. The high boiling
point (242 ◦C) is another advantage of solvent PC as product can be
separated by vacuum distillation [27,38]. In order to reuse rhodium
based catalyst in PC, the hydroformylation experiments with a con-
secutive run were carried out in PC. The reactions were run until
no uptake of syngas was observed to ensure complete conversion
of vinyl acetate as reaction slow down after 90% conversion. The
product was separated from the catalyst/PC by distillation under
reduce pressure and the catalyst/PC was then recycled (Table 5).
Consequently, PC/catalyst system was recycled three times without
significant loss in activity and selectivity.
9000
8750
8500
8250
8000
7750
7500
7250
(a)
500
750
1000
1250
1500
rpm
(b)
Selec.ald.
Selec.branched ald.
100
95
90
85
80
4. Mechanism
500
750
1000
1250
1500
On the basis of experimental results and reported literature
on vinyl acetate hydroformylation, the proposed mechanism
for the rhodium catalyzed hydroformylation of vinyl acetate
using bulky phosphite, P(ONp)3 as ligand is articulated (Fig. 5).
The naphthyl-based monodentate bulky phosphite ligands gave
noticeably high activity and selectivity than phosphine ligands.
Bulky phosphites are weak ␴-donor and strong ␲-acceptor ligands
than phosphine ligands; and are known to enhance the rate of the
hydroformylation reaction [41–44]. The high activity in the case
of bulky phosphite ligand is ascribed to the stronger ␲-acceptor
characteristic and high steric nature, lead to the formation of
monoligated electron deficient rhodium complex, HRh(CO)3L [45].
P(ONp)3, a sterically bulky ligand (cone angle of P(ONp)3 is 166◦
while for PPh3 is 145◦) have high ␲-acceptor character as compare
to PPh3. Under syngas environment reaction solution containing
Rh(acac)(CO)2 and L (L = P(ONp)3) generates catalytically active
species having one P(ONp)3 coordinated to rhodium, HRh(CO)3L
(A) confirmed by in situ IR and NMR [28]. The HRh(CO)3L (A) 18e
complex easily dissociate CO to form species (B), facilitates alkene
coordination and hence enhance rate of reaction. The formation of
16e species (B) is influence by electron-donating or withdrawing
ability of ligands and is in equilibrium with 18e complex (A) (Fig. 5).
The ligand with comparative more ␴-donor ability increases elec-
tron density on rhodium, improves substantial ␲-back donation
to CO, reduce CO dissociation and lead to low rate and selectivity.
The bulky phosphine ligand PNp3 even having high steric nature
was less effective than bulky phosphite in terms of activity and
selectivity. In contrast, ligands with ␲-acceptor capability compete
with CO for the electron back donation. Thus, electron density
rpm
Fig. 4. Effect of stirring rate on TOF (a) and selectivity (b) of vinyl acetate hydro-
formylation catalyzed by Rh/P(ONp)3.
vinyl acetate hydroformylation was studied by varying the stirring
speed (Fig. 4). The other reaction parameters were kept constant.
It was observed that at low stirring rate, the reaction proceeded
slowly with diffusion limitation. Whilst at higher stirring speed,
the CO diffuse rapidly and hence increases the rate of the reaction.
For example, the TOF as well as selectivity were low at lower stir-
ring rate (500 rpm). With an increase in stirring rate from 500 to
950 rpm substantially enhanced both TOF and selectivity (Fig. 4).
These results clearly indicate that the TOF depend on the stirring
rates, particularly when the stirring rate is low. Moreover, at low
stirring speed the formation of byproduct is somewhat higher due
to the slow diffusion of CO. A further increase in stirring rate from
950 to 1350 rpm, no significant changes in TOF and selectivity were
observed. Therefore, in all the experiments the stirring rate was
maintained at 950 rpm.
3.6. Effect of various solvents
The choice of solvent is crucial for a particular reaction to achieve
high activity and selectivity besides the choice of the appropri-
ate ligand. The formation of side products are affected by solvent
used (Table 4). In the cases of conventional organic solvents such
as cyclohexane and toluene, the hydroformylation of vinyl acetate

192
A.A. Dabbawala et al. / Applied Catalysis A: General 419–420 (2012) 185–193
Table 4
Effect of various solvents on Rh/bulky phosphites catalyzed hydroformylation of vinyl acetate.a
Entry
Ligand
Solvent
Toluene
TOF (h−1
)
Saldehyde (%)
b/l
99/1
>99/1
>99/1
>99/1
1
2
3
4
5
6
7
8
P(ONp)3
P(ONp)3
P(ONp)3
P(ONp)3
P(ONp)3
L3
8280
8328
3040
93.0
93.0
93.5
90.5
95
95
95
95
Cyclohexane
DCM
THF
PC
PC
DMC
PC
3200
12240
12120
10320
11760
95/5
95/5
98/2
94/6
L3
L4
a
Reaction conditions: [Rh(CO)2acac], 0.23 mmol/L; P/Rh, 6.0; [vinyl acetate], 0.93 mol/L; temperature, 90 ◦C; syngas pressure (1:1), 4.0 MPa; solvent, 50 mL; reaction time,
10 min.
Table 5
Recycling experiments with the catalyst system (PC/Rh-L3).a
Entry
Catalyst
Conv. (%)
Time (min)
Saldehyde (%)
b/l
1
Rh-L3
100
100
100
100
30
30
40
45
95
95
93
92
95/5
95/5
95/5
93/5
2b
3b
4b
Recycled catalyst
Recycled catalyst
Recycled catalyst
Reaction conditions: [Rh(CO)2acac], 0.23 mmol/L; P/Rh, 6.0; [vinyl acetate], 0.93 mol/L; temperature, 90 ◦C; syngas pressure (1:1), 4.0 MPa; solvent (PC), 50 mL.
The catalyst system was reused after separation of product by vacuum distillation.
a
b
Fig. 5. Proposed mechanism for the rhodium catalyzed hydroformylation of vinyl acetate using P(ONp)3.

A.A. Dabbawala et al. / Applied Catalysis A: General 419–420 (2012) 185–193
193
around metal center decreases thereby increases the reaction rate
References
due to facile CO dissociation and easily alkene association.
In view of above, the vinyl acetate hydroformylation has some
discrete features: (i) vinyl acetate is less reactive to the hydro-
formylation compared to terminal alkenes, (ii) the regioselectivity
of the vinyl acetate hydroformylation is contradictory to that of
non-functionalized linear olefins, the branched aldehyde predom-
inates, and (iii) the reaction rate, regioselectivity and formation
of side products depend distinctly on steric and electric nature
of ligands used. The less reactivity, reversed regioselectivity,
and formation of side products were attributed probably to the
double bond polarization due to the inductive effect of the ester
carbonyl group and chelating effect of the vinyl ester carbonyl
group to metal center. The ester carbonyl group influences the
intermediates stability during hydroformylation by the formation
of thermodynamically stable five and/or six membered rings
through coordination to the rhodium (Fig. 5, species E and E2) and
can slow down carbon monoxide insertion and responsible for the
less hydroformylation reactivity of vinyl acetate and formation of
side products. Consequently, the initial rate of hydroformylation of
vinyl acetate using rhodium complex modified by bulky P(ONp)3
ligand (at 80 ◦C, 3.0 MPa syngas pressure) for vinyl acetate hydro-
formylation) was ∼16 times slower than initial rate of 1-hexene
hydroformylation [28].
[1] C.D. Frohning, C.W. Kohlpaintner, Applied homogeneous catalysis with
organometallic compounds, in: B. Cornils, W.A. Herrmann (Eds.), A Compre-
hensive Handbook in Two Volumes, vol. 1, Wiley-VCH, Weinheim, 1996, pp.
27–104.
[2] P.W.N.M. Van Leeuwen, C. Claver, Rhodium catalyzed hydroformylation,
Kluwer Academic Publishers, Dordrecht, The Netherlands, 2000.
[3] A.A. Dabbawala, D.U. Parmar, H.C. Bajaj, R.V. Jasra, J. Mol. Catal. A: Chem. 282
(2008) 99–106.
[4] B. Breit, Top. Curr. Chem. 279 (2007) 139–172.
[5] F. Ungvary, Coord. Chem. Rev. 251 (2007) 2087–2102.
[6] A.A. Dabbawala, J.N. Parmar, R.V. Jasra, H.C. Bajaj, E. Monflier, Catal. Commun.
10 (2009) 1808–1812.
[7] J.A. Moulijn, P.W.N.W. van Leeuwen, R.A. van Santen, Stud. Surf. Sci. Catal. 79
(1993) 201–216.
[8] A.A. Kaisare, S.B. Owens Jr., E.J. Valente, G.M. Gray, J. Organomet. Chem. 695
(2010) 1472–1479.
[9] A.A. Kaisare, S.B. Owens Jr., E.J. Valente, G.M. Gray, J. Organomet. Chem. 695
(2010) 2658–2666.
[10] A.M. Trzeciak, T. Głowiak, R. Grzybek, J.J. Ziółkowski, J. Chem. Soc., Dalton Trans.
(1997) 1831–1837.
[11] W. Gil, A.M. Trzeciak, J.J. Ziółkowski, Organometallics 27 (2008) 4131–4138.
[12] L.A. van der Veen, P.H. Keeven, G.C. Schoemaker, J.N.H. Reek, P.C.J. Kamer,
P.W.N.M. van Leeuwen, M. Lutz, A.L. Spek, Organometallics 19 (2000) 872–883.
[13] H. Klein, R. Jackstell, K.-D. Wiese, C. Borgmann, M. Beller, Angew. Chem. 113
(2001) 3505–3508.
[14] Y. Yan, X. Zhang, X. Zhang, J. Am. Chem. Soc. 128 (2006) 16058–16061.
[15] S. Yu, Y. Chie, X. Zhang, Adv. Synth. Catal. 351 (2009) 537–540.
[16] C.J. Cobley, K. Gardner, J. Klosin, C. Praquin, C. Hill, G.T. Whiteker, A. Zanotti-
Gerosa, J. Org. Chem. 69 (2004) 4031–4040.
[17] K.N. Bhatt, S.B. Halligudi, J. Mol. Catal. 91 (1994) 187–194.
[18] O. Saidi, J. Ruan, D. Vinci, X. Wu, J. Xiao, Tetrahedron Lett. 49 (2008) 3516–3519.
[19] S. Breeden, D.J. Cole-Hamilton, D.F. Foster, G.J. Schwarz, M. Wills, Angew. Chem.
Int. Ed. 39 (2000) 4106–4108.
5. Conclusions
[20] C.K. Brown, G. Wilkinson, J. Chem. Soc. A (1970) 2753–2763.
[21] B. Fell, M. Barl, J. Mol. Catal. 2 (1977) 301–306.
The naphthyl-based monodentate bulky phosphine and phos-
phite ligands were evaluated in rhodium catalyzed hydroformy-
lation of vinyl acetate. The reaction rate activity and selectivity
(chemo- as well as regio-) depend conspicuously on steric and
electronic nature of ligands. The ligand PNp3 having high steric
nature than PPh3 and offered high regioselectivity toward branched
aldehyde with low activity and low chemo selectivity toward alde-
hyde. While an excellent regioselectivity to branched aldehyde
and high selectivity to aldehyde with high TOF were realized with
monodentate bulky phosphite ligands having ␲-acceptor ability
with comparative more steric nature. Among the naphthyl-based
bulky phosphite ligands, P(ONp)3 afforded notable catalytic activ-
ity. The observed TOF is 3.6 times higher than those observed for
the Rh/PPh3 catalyst. Moreover, the viability and beneficial effect
of organic carbonate as ‘green’ solvent in hydroformylation of vinyl
acetate catalyzed by Rh/bulky phosphites were also investigated.
The substantial advantages of organic carbonates were found com-
pared to the conventional organic solvents and also allow the
recycling of the catalyst.
[22] M. Matsumoto, M. Tamura, J. Mol. Catal. 16 (1982) 195–207.
[23] A.G. Abatjoglou, D.R. Bryant, L.C. D’Esposito, J. Mol. Catal. 18 (1983) 381–390.
[24] A.M. Trzeciak, J.J. Ziółkowski, J. Mol. Catal. 43 (1987) 15–20.
[25] Y.L. Borole, R.V. Chaudhari, Ind. Eng. Chem. Res. 44 (2005) 9601–9608.
[26] P.J. Thomas, A.T. Axtell, J. Klosin, W. Peng, C.L. Rand, T.P. Clark, C.R. Landis, K.A.
Abboud, Org. Lett. 9 (2007) 2665–2668.
[27] D.B.G. Williams, M. Ajam, A. Ranwell, Organometallics 26 (2007) 4692–4695.
[28] A.A. Dabbawala, H.C. Bajaj, R.V. Jasra, J. Mol. Catal. A: Chem. 302 (2009) 97–106.
[29] A.A. Dabbawala, R.V. Jasra, H.C. Bajaj, Catal. Commun. 11 (2010) 616–619.
[30] A.A. Dabbawala, R.V. Jasra, H.C. Bajaj, Catal. Commun. 12 (2011) 403–407.
[31] H. Riihimaki, T. Kangas, P. Suomalainen, H.K. Reinius, S. Jaaskelainen, M.
Haukka, A.O.I. Krause, T.A. Pakkanen, J.T. Pursiainen, J. Mol. Catal. A: Chem.
200 (2003) 81–94.
[32] R.M. Deshpande, R.V. Chaudhari, J. Mol. Catal. 57 (1989) 177–191.
[33] T. Welton, Chem. Rev. 99 (1999) 2071–2083.
[34] P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. 39 (2000) 3772–3789.
[35] R. Sheldon, Chem. Commun. (2001) 2399–2407.
[36] J. Bayardon, J. Holz, B. Schäffner, V. Andrushko, S. Verevkin, A. Preetz, A. Börner,
Angew. Chem. Int. Ed. 46 (2007) 5971–5974.
[37] B. Schäffner, J. Holz, S.P. Verevkin, A. Börner, ChemsusChem 1 (2008) 249–253.
[38] B. Schäffner, V. Andrushko, J. Holz, S.P. Verevkin, A. Börner, ChemsusChem 1
(2008) 934–940.
[39] B. Schäffner, V. Andrushko, J. Bayardon, J. Holz, A. Börner, Chirality 21 (2009)
857–861.
[40] C. Torborg, A. Zapf, M. Beller, ChemsusChem 1 (2008) 91–96.
[41] A. Van Rooy, E.N. Orij, P.C.J. Kamer, P.W.N.M. Van Leeuwen, Organometallics 14
(1995) 34–43.
Acknowledgments
[42] A. Van Rooy, J.N.H. de Bruijn, K.F. Roobeek, P.C.J. Kamer, P.W.N.M. Van Leeuwen,
J. Organomet. Chem. 507 (1996) 69–73.
[43] P.W.N.M. Van Leeuwen, C.F. Roobeek, J. Organomet. Chem. 258 (1983) 343–350.
[44] A. Van Rooy, E.N. Orij, P.C.J. Kamer, F. Van Den Aardweg, P.W.N.M. Van Leeuwen,
J. Chem. Soc., Chem. Commun. 16 (1991) 1067–1096.
Authors are thankful to analytical section of the institute for
assistance with analyses and CSIR and DST for financial support
under CSIR Network Programme NWP 010 and SR/S1/OC-56/2009.
AAD thanks CSIR, New Delhi, for the award of Senior Research Fel-
lowship.
[45] T. Jongsma, G. Challa, P.W.N.M. Van Leeuwan, J. Organomet. Chem. 421 (1991)
121–128.